// (See accompanying file LICENSE_1_0.txt or copy at
//  http://www.boost.org/LICENSE_1_0.txt)

#include <doctest/doctest.h>
#include <fplus/fplus.hpp>
#include <fplus/stopwatch.hpp>

using namespace std::chrono_literals;

template <typename Function>
auto invoke_n_times(int n, Function f)
{
    for (int i = 0; i < n; i++) {
        f();
    }
}

TEST_CASE("Timer - test_accuracy")
{
#ifdef NDEBUG // only on release builds
    using namespace fplus;
    using namespace std::chrono_literals;

    auto measure_delta = []() {
        fplus::stopwatch t;
        std::this_thread::sleep_for(0.05s);
        auto duration = t.elapsed();
        auto delta = duration - 0.05;
        return fabs(delta);
    };

    // we ask for a sleep of 0.05s, but we will have a duration that can be higher
    // (up to 15 ms higher, since the cpu scheduler might switch to another process during this sleep)
    // to account for the cpu/task scheduler
    double max_acceptable_delta__task_scheduler = 0.2;

    // One run
    {
        auto delta = measure_delta();
        REQUIRE_LT(delta, max_acceptable_delta__task_scheduler);
    }

    // 10 consecutive runs (total duration = 0.5 seconds)
    {
        std::vector<double> deltas;
        invoke_n_times(10, [&]() {
            deltas.push_back(measure_delta());
        });
        auto mean_dev = fplus::mean_stddev<double>(deltas);
        REQUIRE_LT(mean_dev.first, 0.15);
        REQUIRE_LT(mean_dev.second, 0.07);
    }
#endif
}
